Examination and diagnosis
  1. Examination and diagnosis

Examination and diagnosis

The diagnosis of CML is confirmed by blood and bone marrow tests. In case of CML, the blood contains a large number of white blood cells. The bone marrow will also show an increase in these cells. To definitively diagnose CML, the Philadelphia chromosome (the genetic disorder that causes CML) must be demonstrated by chromosome testing or a so-called PCR test.

Blood cells

Blood testing

Blood consists of:

  • Red blood cells: for oxygen transport
  • White blood cells: for defence against infections
  • Platelets: for blood clotting

During the blood test, a small vial is filled with blood taken from a vein in the arm. The vial is sent to the laboratory, where a device determines the quantity and quality of the specific blood cells. In case of CML, the sample will contain far too many white blood cells.

Bone marrow testing

Bone marrow is the place where blood cell production takes place and is located in the marrow cavities of the bones. For bone marrow testing, the back of the pelvis and sternum are the easiest and safest places to obtain it. This is called a bone marrow puncture.

The physician first administers a local anesthetic. Bone marrow cells are then aspirated from the hollow part of the bone with a needle. Some people feel a dull or sharp pain when the sample is taken, but this does not last longer than a few seconds. In total, the whole procedure takes about 10 to 15 minutes. After the procedure, the puncture site may be a little sensitive. 

In case of CML, too many white blood cells are found in the bone marrow, just like in the blood. The bone marrow is also examined for the presence of the Philadelphia chromosome, the abnormal chromosome that causes CML.


The PCR test is a molecular test to determine the quantity of the BCR/ABL gene. This gene causes the production of the BCR/ABL protein, the protein that causes the bone marrow cells to divide far too much. The PCR test is the most accurate test available and is therefore used as definitive confirmation of the CML diagnosis. The test can be done with both blood and bone marrow but is usually performed with blood. This test is also important during treatment to monitor the response to treatment.